Decision at Sundown was one of several felicitous collaborations between star Randolph Scott and director Budd Boetticher. Scott plays a flint-eyed gunman who rides into a sleepy town to drive out local tough guy John Carroll by sundown. Scott is motivated not by justice but by revenge; years earlier, Carroll had stolen Scott's wife. The woman subsequently killed herself, and the fact that she had left Scott willingly is torturing both men, each of whom feels partially responsible for her death. As sundown approaches, the "angst" suffered by both hero and villain spreads to the rest of the townspeople, who do a lot of soul-searching while waiting for the final confrontation. Decision at Sundown truly lives up to the label "psychological western".
~ Hal Erickson, All Movie Guide